PHP problems

<?php


// username and password sent from form
$username=stripslashes($_POST['myusername']);
$password=sha1(stripslashes($_POST['mypassword']));


$host="localhost"; // Host name
$username="bluecode_power"; // Mysql username
$password="bluecode123"; // Mysql password
$db_name="bluecode_login"; // Database name
$tbl_name="members"; // Table name

// Connect to server and select databse.
mysql_connect("$id", "$username", "$password")or die("cannot connect");
mysql_select_db("$db_name")or die("cannot select databse");

$sql="SELECT * FROM `members` WHERE myusername=='$username' and mypassword=='$password'";

// Mysql_num_row is counting table row
$count=mysql_num_rows($result);


if($myusername == admin){
session_register("myusername");
session_register("mypassword");
header("location:login_success.php");
}

// If result matched $myusername and $mypassword, table row must be 1 row
if($count==1){



// Register $myusername, $mypassword and redirect to file "login_success.php"
session_register("myusername");
session_register("mypassword");
header("location:login_success.php");
}

else {
echo "Wrong Username or Password";
}
?>